1. Field of the Invention
The present invention relates generally to sequence switches that are provided with a forced disconnect capability and, more particularly, to a double-pole double-throw switch that moves a first set of movable contacts prior to a second set of movable contacts and then forces the movement in the event that a failure of some type prevented the normal movement of the contacts.
2. Description of the Prior Art
Many different types of switches are well known to those skilled in the art. In addition, it is also known to provide a switch with a forced disconnect capability. This capability is also referred to as a positive break capability. The purpose for a forced disconnect characteristic in a switch is to mechanically force the movable contacts away from the stationary contacts in the event of a switch failure wherein the movable and stationary contacts become welded together. In switches that do not have this positive break characteristic, the movable and stationary contacts can be welded together and, even though the switch mechanism attempts to open the electrical connection, the movable and stationary contacts remain in electrical communication with each other because they are welded together. A positive break characteristic provides an additional mechanism that is able to force the disconnection of the movable and stationary contacts mechanically and break the weld connection.
U.S. Pat. No. 5,283,406, which issued to Olsen on Feb. 1, 1994, discloses a switch with a movable carrier to which movable contacts are attached. The switch is provided with a movable contact and a contact carrier that significantly facilitates the manufacturing process that is necessary to make the assembly. The contact carrier is provided with first and second extensions that are generally flexible and associated with each other to provide a gap therebetween. In the preferred embodiment of the device, the second extension comprises first and second fingers that extend from the contact carrier. The second extension is provided with protuberances that permit a movable contact to deform the second extension as it is moved inward toward the contact carrier. The extensions snap together after the complete movable contact has moved into a predetermined space between the extensions. The assembly of the present invention permits the movable contact to be permanently retained between the first and second extensions, but variably movable in position within that containment to permit the position of the movable contact to adjust to the position of the fixed contact with the contact carrier is moved within a housing structure to force the movable contacts into electrical communication with a pair of fixed contacts. The switch described in the. Olsen patent is a double-pole double-throw switch. In addition, it illustrates a positive break mechanism that comprises rotatable cams that can force the contacts open even though they may be welded together.
Sequence switches are known to those skilled in the art. The purpose of a sequence switch is to cause one set of movable and stationary contacts to move relative to each other prior to a similar relative movement between another set of stationary and movable contacts. When a switch of this type is connected to electrical circuitry, a first circuit can be energized or deenergized prior to a similar change in another circuit. The switch described in the Olsen patent does not provide this sequencing capability. Because of the necessity for a sequence switch to actuate or de-actuate one set of contacts prior to another set of contacts, the forced disconnect capability, or positive break capability, has not been implemented in sequencing switches. It would therefore be significantly beneficial if the capability to provide a forced disconnect mechanism was available in a sequence switch.